Thermal insulation device for at least one underwater pipe compressing sealed partitions

ABSTRACT

The present invention concerns a device ( 1 ) for heat-insulating at least one sub-marine pipe ( 4 ) comprising:  
     a heat insulation covering ( 3 ) surrounding said pipe(s) ( 3 ),  
     said covering being covered by a sealed protective envelope ( 2 ), and  
     said envelope having a tubular shape and a longitudinal axis of symmetry (ZZ′);  
     said insulation covering ( 3 ) including a material subject to migration and said envelope ( 2 ) being constituted by a flexible or semi-rigid material able to remain in contact with the external surface of said insulation covering ( 3 ) when the latter warps.  
     said device being characterised in that it includes at least two sealed transversal partitions ( 5 ), each of said partitions being constituted by a closed rigid piece traversed by said pipe(s) and integral with the latter and integral at its periphery with said envelope.

[0001] The present invention concerns device and method forheat-insulating at least one sub-marine pipe situated at a great depth.

[0002] More particularly, it concerns the pipes connecting the bottom ofthe sea to anchored installations floating on the surface.

[0003] The technical sector of the invention is the field concerning theproduction and mounting of insulation systems outside and around pipesin which hot effluent circulates for which it is desired to limit heatlosses.

[0004] This invention is more particularly applicable to thedevelopments of deep sea petroleum fields, that is petroleuminstallations installed in the sea in which the surface equipment isgenerally situated on floating structures, the well heads being at thebottom of the sea. The pipes concerned by the present invention moreparticularly are risers or surface/bottom linking pipes rising to thesurface, but also pipes connecting the well heads to said surface/bottomlinking pipes.

[0005] Deep sea developments are carried out by water depths currentlyreaching 1500 m. Future developments are envisaged by water depths up to3000-4000 m and beyond.

[0006] The main application of the invention concerns the heatinsulation of sub-marine or sub-aquatic immersed pipes or ducts andsituated more particularly at a depth of more than 300 metres andcarrying hot petroleum products whose excessive cooling would causeproblems during normal production and when production is stopped.

[0007] In fact, in these types of applications, many problems occur ifthe temperature of the petroleum products reduces by a significant valuewith respect to their production temperature which is often more than 60to 80° C. when the temperature of the surrounding water at a great depthmay be basically lower than 10° C. and reach 4° C. If the petroleumproducts cool below 30-60° C. for an initial temperature of between 70and 80° C., the following is generally observed:

[0008] a high increase of viscosity which then reduces the flow of thepipe,

[0009] a precipitation of dissolved paraffin which then increases theviscosity of the product and whose deposit can reduce the internaleffective diameter of the pipe,

[0010] the flocculation of asphaltenes bringing about the same problems,

[0011] the sudden, compact and massive formation of gas hydrates whichprecipitate at high pressure and at a low temperature, thus suddenlyblocking off the pipe.

[0012] Paraffins and asphaltenes remain stuck to the wall and then needto be cleaned by scraping the inside of the pipe. On the other hand, thehydrates are even more difficult and sometimes impossible to resorb.

[0013] The aim of the heat insulation of these pipes is therefore todelay cooling of the petroleum effluent carried, not only duringestablished production mode so that their temperature is for example atleast 40° C. when arriving on the surface for a production temperatureat the inlet of the pipe of between 70 and 80° C., but also in cases ofa reduction or even stoppage of production so as to ensure that thetemperature of the effluent does not go below for example 30° C. so asto limit the problems mentioned above or at least enable them to berendered reversible.

[0014] In the case of the installation of single pipes or bundles ofpipes, said pipes are generally preferably prefabricated on shore inunit lengths of between 250 and 500 m which are then drawn from the opensea with the aid of a tow boat. In the case of a tower typebottom/surface link, the pipe length generally represents 50 to 95% ofthe water height, that is it can reach 2400 m for a water depth of 2500m. When produced on shore, the first unit length is pulled from the seaand joined end-to-end to the next one, the tow boat keeping the unit intraction during the adding-on phase which may last several hours or evendays. When the whole pipe or bundle of pipes has been placed in thewater, the unit is pulled up to the site, generally on the subsurfaceapproximately horizontal where it is then “canted”, that is tilted intoa vertical position, so as to reach the vertical position and then beingplaced into its final position.

[0015] A known insulation device exists having at least one sub-marinepipe (which may in fact be a single pipe or assembled with other pipesthus constituting bundles) to be placed on the bottom at a great depthand comprising an insulation external covering surrounding it and aprotective envelope.

[0016] The insulation of the pipe(s) or pipe bundle commonly known as“bundles” is/are then protected by an external envelope having a doublefunction:

[0017] firstly avoiding damage which may occur when producing or towingas in placing, especially in shallow water zones, said towing able incertain cases to be effected over distances ranging up to severalhundreds of kilometres. To this effect, relatively resistant materialsare used, such as steel, thermoplastic or duroplastic compounds or evena composite material;

[0018] secondly creating a sealed containment around the insulationsystem. This containment is required for external insulation coveringsconstituted by materials subject to migration including fluid compounds.

[0019] In effect, through sea bottoms of 2000 m, the hydrostaticpressure is about 200 bars, namely 20 megapascals, which requires thatall the pipes and their insulation coverings need to be able to resist,not only these pressures without deteriorating during pressurisationsand depressurisations of the pipe in which the hot fluid circulates, butalso temperature cycles which generate volume variations of the variouscomponents and thus of positive or negative pressures possibly resultingin the partial or total destruction of the envelope, either by exceedingthe admissible stresses or by this external envelope imploding (negativeinternal pressure variations).

[0020] The patents FR99/00985 and WO 00/40886 describe a method anddevice concerning a solid/liquid phase change and melting latent heatinsulation material able to restore calories in the internal pipe andconfined inside a sealed ductile envelope which makes it able to followthe expansion and contraction of the various components under theinfluence of all the environment parameters, including the internal andexternal temperatures. Thus, the pipe is confined inside a flexiblethermoplastic envelope, possibly circular, made in particular ofpolyethylene or polypropylene, the increase or reduction of the internalvolume due to the temperature variations and comparable to respirationbeing absorbed by the flexibility of the envelope constituted, forexample, by a thermoplastic material having a large elastic limit. So asto resist the mechanical stresses, a semi-rigid envelope is preferablyused constituted by a resistant material such as steel or a compositematerial, such as a compound embodied from a binder such as an epoxyresin and mineral or organic fibres such as glass or carbon fibres, butthe bundle here is given an ovoid or flattened shape with or without anycounter curve which on a constant perimeter provides it with a sectionsmaller than the corresponding circle. Thus, the “respiration” of thebundle shall result, in the case of an increase and reduction of thevolume in respectively a “recircling” of the envelope or an accentuationof flattening of the envelope. In this case, the bundle/envelope unit isdenoted by the term “flat bundle”, as opposed to a circular envelope.

[0021] There is also the method used on the GANET field which consistsof prefabricating onshore a sealed circular bundle having no insulatingcomplex but filled with an inert gas and then of towing it onto the siteand installing it at great depth so as to finally fill it with amono-ethylene glycol-based insulating compound added withviscous-rendering agents. So as to absorb the volume variations createdby the temperature variations without creating unacceptable stressesinside the circular steel envelope, a ductile pipe pressurised withnitrogen has been installed inside the bundle along the latter.

[0022] These prior embodiments have been described for applications inwhich the pipe rests horizontally on the bottom of the sea

[0023] In the case of a bottom/surface link, for example the verticalportion of a tower or even the small chain section connecting the top ofthe tower to the surface support or even pipes resting on a steep slopeof the bottom of the sea, the external pressure varies along the pipeand gradually decreases when it is brought back up to the surface. Inthe case of fluid or pasty insulating materials, when this bottom has adensity less than that of the water of the sea, generally a density ofbetween 0.8 and 0.85, the differential pressure between the outside andthe inside shall vary along said pipe and gradually increasing when itis lifted up to the surface. Thus, this results in deformationsaccentuated in those portions exhibiting the differential pressuremaximum, thus inducing significant transfers of fluid parallel to thelongitudinal axis of said pipe. In addition, the transfers are amplifiedby “breathing” phenomena due to the temperature variations describedabove.

[0024] A “flat bundle” is sensitive to the pressure variations due tothe slopes: excess pressure at the bottom, depression at the top, andthe pulling phase is critical as the length, possibly reaching severalkilometres, the bundle is never made to be perfectly horizontal and thisresults in significant differential pressure variations during towingand particularly during the canting operation.

[0025] When the bundle is in the vertical position or at the bottom ofthe sea on a steep slope, the pressure differential created by the lowdensity of the insulating material associated with the volume variationcreated by the heat expansion of the insulation material generatesmovements of the insulating material the external envelope needs to beable to support. Thus, efforts are sought to avoid the movements ofparticles parallel to the axis of the bundle, that is migrations of theinsulation material between two distant zones of the bundle as they riskdestroying the actual structure of the insulating material.

[0026] So that the bundle behaves properly throughout its stay at sea,it is desirable that it does not comprise any residual gas. In fact, inthe case of a semi-fluid or pasty insulating complex, any pocket of gasresulting from the production process shall have repercussions, firstlyconcerning transport as, the moment the bundle is moved to a significantdepth, the ambient pressure compresses the residual gas which riskssignificantly reducing buoyancy, this possibly leading to dangeroussituations, not only for the materials but also for personnel; andsecondly, during vertical positioning, all the compressed gas pocketsmove to the top of the bundle, thus risking creating a significant pipelength without any insulating component.

[0027] The object of the present invention is to be able to produce atthe best possible cost a “bundle” onshore, of being able to place acovering made of a pasty or semi-fluid insulating material, of towing itto the subsurface, of canting it into a vertical position so as toinstall it whilst observing the completeness of the unit until its isput into production and throughout its period of life which generally ismore than 30 years.

[0028] A further object is to be able to embody the insulation of atleast one sub-marine pipe to be laid on the sea bottom at great depthand in particular in zones with steep slopes from a sealed “flat bundle”type envelope able to provide significant transversal flexibility so asto absorb volume variations whilst retaining sufficient longitudinalrigidity so as to authorise handlings, such as onshore preproduction,towing to the site and the preservation of the mechanical integrity ofsaid envelope throughout the period of life of the product which reachesand exceeds 30 years.

[0029] The problem to be resolved is to minimise the longitudinalmigrations of the insulation materials subject to migration which isparticularly significant when said insulating material is a semi-fluidor pasty, especially of the jellified insulation matrix type, owing tothe risks of deteriorations of the performances of the insulationcomplex the moment inappropriate internal shearings are applied to saidinsulation matrix.

[0030] To reach this aim, the present invention concerns a heatinsulation device having at last one sub-marine pipe comprising:

[0031] a heat insulation covering surrounding said pipe(s),

[0032] said covering being covered with a sealed protective envelope,and

[0033] said insulation covering including a material subject tomigration and said envelope being constituted by a flexible orsemi-rigid material able to remain in contact with the outer surface ofsaid insulation covering when the latter warps,

[0034] said envelope has a tubular shape and having a centrallongitudinal axis ZZ′ and preferably the transversal section of saidenvelope defining a perimeter having two axes of symmetry XX′ and YY′perpendicular to each other and to said longitudinal axis ZZ′.

[0035] According to a first main characteristic, the device of theinvention is characterised in that it includes at least two sealedtransversal partitions each being constituted by a closed rigidstructure traversed by said pipe(s) and integral with the latter and atits periphery with said envelope.

[0036] This rigid structure integral with the envelope prevents themovement of said envelope opposite said partition and with respect tothe latter and thus fixes the geometry of the cross section of theenvelope at the level of said partition.

[0037] The terms “sealed” and “closed” is understood to mean that saidpartition does not allow the material constituting said insulationcovering to pass through said partition and in particular that thejoining point between said pipe and the orifices through which said pipetraverses said partition prohibits the passage of said material of theinsulation covering.

[0038] The sealed partitions ensure the containment of the insulatingmaterial constituting said insulation covering between said envelope andsaid partitions.

[0039] The term “cross section” is understood to be the section inside aplane XX′, YY′ perpendicular to said longitudinal axis ZZ′ of saidenvelope.

[0040] In a particular embodiment, said closed structure of said sealedtransversal partition includes a cylindrical piece having a crosssection whose perimeter has the same fixed shape as that of said crosssection of the envelope.

[0041] The term “perimeter of the cross section” is understood in thepresent description to be the closed curve-shaped line which delimitsthe flat surface defined by said cross section.

[0042] The perimeter of the cross section of the envelope at the levelof the sealed partitions has a fixed shape and is thus unable to warpvia contraction or expansion of said envelope at this level.

[0043] According to various embodiment variants, said cross section ofthe envelope has a circular or oval or even rectangular shape andpreferably with rounded angles.

[0044] Where the device comprises at least two pipes arranged along agiven plane, the cross section of said envelope has preferably anelongated shape in the same direction as this plane.

[0045] More particularly, the external perimeter of the cross section ofsaid protective envelope is a closed curve whose ratio of the square andlength on the surface it delimits is at least equal to 13, as describedin FR99/00985.

[0046] During internal volume variations, the envelope shall tend towarp into having a circular shape which mathematically constitutes theshape having at a constant perimeter the largest surface.

[0047] In the case of a sealed envelope with a circular profile, avolume increase generates stresses in the wall which are linked to thepressure increase resulting from this volume increase.

[0048] On the other hand, if the shape of the cross section of theexternal covering is flattened, the better is the capacity of itsenvelope to absorb the expansions due to the dilation of the variouscomponents under the effect of the temperature without creating anysignificant excess pressure as the envelope then is able to be rounded.

[0049] In the case of a profile with an oval shape, an internal pressurevariation shall involve a combination of bending and pure tractionstresses as the variable curve of the oval then behaves as anarchitectural arch with, however, the difference that in the case of ourenvelope, the stresses are traction stresses and not compressionstresses. Thus, an oval shape or one approaching an oval shall be ableto be envisaged for low expansion capacities and it shall be appropriateto then consider ovals with a length ratio of the major axis pmax tothat of the minor axis pmin as high as possible, such as at least 2/1 or3/1.

[0050] Then the shape of the envelope shall be selected according to theoverall expansion of the volume of the external insulation coveringunder the effect of temperature variations. Thus, for an insulationsystem mainly using materials subject to expansion a rectangular,polygonal or even oval shape allows an expansion via bending of the wallwhilst inducing a minimum of traction stresses in the external envelope.

[0051] For an insulation material possessing large expansion under theeffect of temperature variations, such as gas oil, products of thefamily of alcanes (paraffins) or even phase change materials, therectangle shall advantageously be flattened so as to create thenecessary expansion reserve. It is possible to further increase thisexpansion reserve by creating by known means counter-curves.

[0052] “Insulating material” is understood here to be a materialpreferably having a heat conductivity of less than 0.5 W×m×K andpreferably between 0.05 and 0.2 W×m×K. K (Watt/metre/Kelvin).

[0053] The term “material subject to migration” is understood to be aliquid, pasty or solid consistency material, such as the consistency ofa grease, paraffin or gel able to be deformed by the stresses resultingfrom differential pressures between two separate points of the envelopeand/or temperature variations inside said insulation material.

[0054] There exist various heat insulation materials able to constituteinsulation coverings according to the invention.

[0055] Most frequently, this involves insulation complexes including afirst compound, such as a hydrocarbonated compound like paraffin or gasoil, and preferably mixed with a second gelling compound and/or with astructuring effect, especially by means of reticulation, such as asecond compound of the polyurethane type.

[0056] As first compounds, it is possible to cite more particularly thechemical compounds of the family of alcanes, such as paraffins or waxes,bitumen, tars, thick alcohols, glycols and more particularly evencompounds whose temperature for melting materials is between thetemperature t₁ of the hot effluent circulating in one of the pipes andthe temperature t₂ of the surrounding medium of the pipe in operation,namely in fact generally speaking a melting temperature between 20 and80° C. As a paraffin for example, tetracosane is used having the formulaC₂₄H₅₀ having a melting temperature of about 50° C.

[0057] Said partitions create heat bridges. Thus, it is necessary tospace the partitions as much as possible so as to reduce the heatbridges.

[0058] In a particular embodiment, the spacing between two successivesealed partitions along said longitudinal axis ZZ′ of said envelope isbetween 50 and 200 metres and in particular between 100 and 150 metres.

[0059] So as to reduce the number of sealed partitions, according to onepreferential characteristic, a device according to the inventionincludes at least and preferably a plurality of cooling jig(s) disposedtransversally to said longitudinal axis (ZZ′) constituted by an openrigid structure integral with said pipe(s) and traversed by the latterand integral with said envelope at its periphery and placed between saidtwo successive sealed partitions preferably at regular intervals alongsaid longitudinal axis ZZ′, said cooling jig preferably having openingsallowing the passage of the material constituting said insulationcovering through said cooling jig.

[0060] Like said sealed partition, said cooling jig fixes the shape ofthe cross section of the envelope at the level of said cooling jigwhilst at the same time minimising the heat bridges.

[0061] More particularly, said open structure of said cooling jigincludes a cylindrical piece having a cross section whose perimeter isinscribed in a geometrical figure identical to the geometrical figuredefined by the shape of the perimeter of the cross section of saidsealed partition.

[0062] A device of invention preferably comprises a plurality of coolingjigs placed along said longitudinal axis ZZ′ of the envelope andpreferably at regular intervals, two successive cooling jigs beingspaced preferably between 5 and 50 metres and better still between 5 and20 metres.

[0063] According to a second main characteristic of the presentinvention, the device includes at least one centralising jig andpreferably a plurality of centralising jigs placed transversally to saidlongitudinal axis ZZ′ at regular intervals between two said successivesealed partitions and/or between said two cooling jigs along saidlongitudinal axis ZZ′, each centralising jig being constituted by arigid piece integral with said pipe(s) and having a shape permitting alimited movement of said envelope on contraction and on expansion withrespect to said centralising jig, said rigid piece of the centralisingjig having an external surface, preferably a cylindrical externalsurface in which the perimeter of the cross section stands back withrespect to that of said sealed partition and limits the warpings of saidenvelope by a mechanical stop on at least two opposing points of theperimeter of the cross section of said envelope.

[0064] This centralising jig is used to ensure a minimum coating of theinsulation covering (3) around said pipe(s) in cases of warping viacontraction of the envelope and transfer of said material able to flowbetween said two sealed partitions and/or between said two cooling jigs.

[0065] More particularly, said centralising jig has a cross sectionwhose perimeter is inscribed inside a geometrical figure which isapproximately homothetic with respect to the geometrical figure definedby the perimeter of the cross section of said sealed partition.

[0066] In one embodiment, said rigid piece constituting saidcentralising jig has one portion of its external surface sufficientlystanding back with respect to the surface of the envelope and/or hasperforations traversing it so as to create a space allowing the transferof the material constituting said insulation covering through saidcentralising jig.

[0067] The distance between two centralising jigs along saidlongitudinal axis ZZ′ is such that it makes it possible to ensureretaining a quantity of material constituting said insulation coveringsufficient to ensure the minimum coating required for the heatinsulation of said pipe, having regard to the deformations oncontraction supported by said envelope.

[0068] Advantageously, the device of the invention comprises a pluralityof centralising jigs and two successive centralising jigs are spacedalong said longitudinal axis ZZ′ of the envelope by a distance ofbetween 2 and 5 metres.

[0069] The present invention more particularly concerns a deviceincluding at least two sub-marine pipes placed in parallel.

[0070] In this case, said sealed partitions of the cooling jig andcentralising jig advantageously keep at least said two sub-marine pipesat a fixed distance from each other.

[0071] The present invention also concerns a unit heat insulation devicefor obtaining a device according to the invention by assembling end toend said unit heat insulation devices and is characterised in that itincludes:

[0072] one or the unit elements of the sub-marine pipe instead of thesub-marine pipes, and

[0073] an insulation covering and said protective envelope as definedabove, each said unit element including, from at least one of itsextremities or at each of its extremities said sealed partition andpreferably from said centralising jigs and again preferably from thecooling jigs as defined above arranged between two successive sealedpartitions.

[0074] Finally, the present invention concerns a method for heatinsulating at least one sub-marine pipe characterised in that unit heatinsulation devices described above are embodied and are assembled end toend as described above.

[0075] In one preferred embodiment, said insulation material is acomplex including various components which are mixed and then injectedin a liquid state into various compartments delimited by said twosuccessive sealed partitions and said insulation material is transformedinto a gel by the reticulation of at least one of its components.

[0076] This type of jellified matrix is able to limit convection.

[0077] Other characteristics and advantages of the present inventionshall appear more readily from a reading of the following descriptiongiven by way of non-restrictive illustration with reference to theaccompanying drawings on which:

[0078]FIGS. 1, 2 and 3 are cutaway views of a cross section of a bundlein which the cross section of the envelope has a circular shape (FIG.1), rectangular with rounded edges (FIG. 2) and oval (FIG. 3).

[0079]FIG. 4 is a side view of a device according to the invention inthe case of an application in a rising column.

[0080]FIGS. 5, 6 and 7 are cutaway views showing the cross section ofthe device at the level a-b-d and e of FIG. 4 respectively for each ofthe types of devices with a circular envelope (FIG. 5), oval envelope(FIG. 6) and a rectangular envelope with rounded edges (FIG. 7).

[0081]FIGS. 8, 9 and 10 represent the various states for obtaining adevice with an oval envelope (FIG. 10) from a device with a circularenvelope (FIG. 8) by embodying warping beyond the elastic limit (FIG.9).

[0082]FIGS. 11, 12 and 13 are cutaway views of a cross section of adevice with an oval envelope at the level of a sealed partition (FIG.11) and at the level of a centralising jig (FIGS. 12 and 13), saidenvelope being in a contraction phase (FIG. 12) and in an expansionphase (FIG. 13).

[0083]FIG. 14 is a side view of a device according to the inventionhaving several centralising jig and cooling jig sealed partitions.

[0084]FIGS. 15, 16 and 17 represent a cutaway view of a cross section ofa device according to the invention including a rectangular envelopewith rounded angles at the level of a centralising jig respectively inan idle position (FIG. 15), in the expansion configuration of theenvelope (FIG. 16) and in the contraction configuration of the envelope(FIG. 17).

[0085]FIGS. 18 and 19 respectively represent the cutaway view (FIG. 18)and side view (FIG. 19) of a device according to the invention includinga rectangular envelope with rounded edges equipped with an externalscreen giving it a circular shape, the small screen being equipped withantivortex helixes.

[0086]FIG. 20 is a longitudinal cutaway view of a device according tothe invention having a sealed partition, a centralising jig and acooling jig.

[0087]FIGS. 21 and 22 respectively represent a longitudinal cutaway view(FIG. 21) and top view (FIG. 22) of a centralising or cooling jigincluding a rigid piece with a bicycle type open structure with spokes.

[0088]FIGS. 8, 9 and 10 represent the section of the external steelenvelope of a bundle, respectively its circular shape followingproduction (FIG. 8), then deformed beyond the elastic limit with thepress under a force F and finally in a slightly flattened shape afterreleasing the force F (FIG. 9) which then constitutes the externalenvelope of a “flat bundle” having an approximately oval section (FIG.10).

[0089]FIG. 1 is the cutaway view of the cross section of a deviceaccording to the invention, and is composed of a flexible circularexternal envelope 2 made of a thermoplastic material containing aninsulation material 3 subject to migration, for example a pasty paraffintype material , at the centre of which are placed two petroleum effluentproduction pipes 4, as well as an auxiliary heating pipe 15 and anelectric cable 16.

[0090] In FIGS. 2 and 3, the same pipes 4 and 15 and cables 16 areplaced inside a flat bundle made of sheet steel or a composite material,the external envelope 2 respectively having the shape of a rectanglewith rounded edges (FIG. 2) or approximately the shape of an ellipse(FIG. 3).

[0091]FIG. 4 is a front view of a thermically insulated rising columnportion or “riser” 1 comprising an external envelope 2 made of either athermoplastic material or of steel or even of a composite material whosesection can be circular as shown in detail on FIG. 5 or elliptic asshown in detail on FIG. 6 or even rectangular with rounded edges asshown in detail on FIG. 7.

[0092] Said riser 1 comprises two pipes 4 installed at the centre, aswell as a sealed partition 5 at the upper portion (a) and lower portion(b) used to contain in cooperation with the external envelope 2 theinsulating material 3. Said sealed partition 5 supports said pipes 4 andkeeps them away from each other by a fixed distance and from the wall.

[0093] All the figures show a heat insulation device with two sub-marinepipes comprising a heat insulation device with at least one sub-marinepipe comprising:

[0094] an insulation covering surrounding said pipe(s),

[0095] said covering being covered with a protective envelope, and

[0096] said envelope having a tubular shape and a longitudinal axis ofsymmetry ZZ′, the cross section of said envelope defining a perimeterhaving two axes of symmetry XX′ and YY′ perpendicular to each other andto said longitudinal axis ZZ′.

[0097]FIGS. 4 and 14 show a portion or section of a heat insulationdevice 1 designated above as a unit heat insulation device whichincludes two sealed partitions 5 and a plurality of centralising jigs 6or cooling jigs 7. The sealed partitions 5, centralising jigs 6 andcooling jigs 7 are rigid pieces having a cylindrical shape, as shown onFIG. 20.

[0098] On FIGS. 5, 6, 7 and 11, the rigid piece constituting the sealedpartition has a cross section having the same shape as that of the crosssection of the envelope. On FIG. 20, the height of the cylindrical rigidpiece constituting the sealed partition 5 is at least one quarter andpreferably about half its diameter so that the contact surface 5,together with the envelope by which the sealed partition is renderedintegral with the envelope, is sufficiently large. The sealed partition5 is traversed by the pipes 4. The link between the sealed partition andthe pipes 4 is also sealed which renders possible containment withoutany leaks occurring inside the envelope of the insulation material. Thesealed partition 5 has mechanical resistance to enable it to fix thesection of the external envelope to this level (levels a and d, FIG. 4).The external cylindrical surface 5 ₁ of the rigid piece constituting thesealed partition 5 is glued or welded to the envelope, butadvantageously it can also be as a complement encircled by an externalcircling strip 18 outside the envelope at this level.

[0099] Said sealed partitions are structures separate from said envelopehaving a continuity in a longitudinal direction between two pointssituated on both sides of said partition.

[0100] Placed inside the confined space between two sealed partitions 5of said section 1 ₁ are firstly centralising jigs 6 and secondly coolingjigs 7.

[0101] The centralising jigs are preferably placed at regular intervals,for example by a distance of between 2 and 5 metres. They are alsocomposed of a rigid piece integral with the internal pipes 4, the shapeof the centralising jigs permitting a limited movement of the envelope 2on contraction and on expansion opposite said centralising jig 6. Moreparticularly, said movement of the envelope 2 opposite said centralisingjig 6 represents a variation of between 0.1 and 10% and preferablybetween 0.1 and 5% of the distance between two opposing points 2 ₁-2 ₂,2 ₃-2 ₄ of the perimeter of the cross section of said envelope.

[0102] On FIGS. 15 to 17, said cross section of said centralising jig 6has the shape of a rectangle whose angles are truncated into bevels 9 ₁.

[0103] On FIGS. 12 and 13 and 15 to 17, the centralising jig has a crosssection whose perimeter is inscribed inside a first geometrical figure6₁ having the shape of a rectangle with rounded edges (FIG. 15), ovalshape (FIG. 12) which is homothetic with respect to the geometricalfigure defined by the perimeter of the cross section of the sealedpartition with which it cooperates.

[0104] On FIGS. 16 and 17, these show that the perimeter of the crosssection of the centralising jig 6 stands back with respect to that ofthe sealed partition and thus of the envelope in idle position (FIG. 11)and limits the deformations (FIGS. 16 and 17) of said envelope via adirect mechanical stop of the latter on at least two opposing points 2₁-2 ₂, 2 ₃-2 ₄ of the perimeter of the cross section of said envelope.

[0105] In the event of excess pressure inside the envelope with respectto the outside (see zone b FIGS. 4 and 16), if the envelope 2 is notcircular and has a flattened shape, especially oval or rectangular witha major axis of symmetry XX′ and a minor axis of symmetry YY′perpendicular to each other and situated inside the cross section plane,the perimeter of the cross section of the envelope tends to becircularised. In these circumstances, the mechanical stop and thus thecontact of the envelope with said centralising jig is then made only atopposing points 2 ₁-2 ₂ of said envelope situated on the largest majoraxis of symmetry XX′ so that the expansion of said envelope along theminor axis of symmetry XX′ is also limited (see zone b of FIGS. 4 and16) and the cross section of said envelope can thus stay with aflattened shape (not-circular).

[0106] On the other hand, in the case of excess pressure of the outsideof the envelope with respect to the inside of the envelope, themechanical stop and the contact of the envelope with said centralisingjig is made both at opposing points 2 ₁-2 ₂ of said envelope situated onthe largest major axis of symmetry XX′ and at opposing points 2 ₃-2 ₄ ofsaid envelope situated on the smallest minor axis of symmetry YY′ insidethe cross section plane so that the contraction of said envelope islimited (see zone d of FIGS. 4 and 17). Thus, any possible implosion ofthe envelope is avoided at these points.

[0107] The centralising jig 6 advantageously has at its periphery,mainly in the zones in contact with the envelope, a sufficiently widecontact surface 6 ₄ so as to avoid damaging the external envelope 2 whenthe bundle “breathes”. On the other hand, the central portion of thecentralising jig can be hollowed 6 ₅, as shown on FIG. 20, so as tominimise the heat points whilst sufficiently retaining enough materialto preserve the centralising jig with sufficient rigidity.

[0108] The cooling jigs 7 are thinner cylindrical rigid pieces, theirfunction, like the sealed partitions 5, being to fix the shape of thecross section of the envelope at their level, this section preferablybeing identical to the one imposed by the sealed partition 5. Thecontact surface 7 ₂ of the peripheral section of the cylinderconstituting the piece thus, as shown on FIG. 20 has a height smallerthan those of the centralising jigs or sealed partitions so as tominimise the heat points, but like the sealed partitions, they arerendered integral with the envelope by glueing or welding and preferablyby tying up (7 ₂) with a tying up strip outside the envelope 18.

[0109] The cooling jig 7 is not sealed as it comprises openings 7 ₁which allow the insulating material to pass, especially during theinsulation material filling phase, said material being fluid or pastyand preferably having an extremely low viscosity. The cooling jig 7 isintegral with the internal pipes 4 and keeps them at a fixed distancefrom each other like the sealed partitions 5 and the centralising jigs6. The cooling jig also keeps the internal pipes at fixed distances fromthe envelope at the level of the cooling jig.

[0110] The successive cooling jigs are preferably spaced by a distanceof between, 5 and 50 metres and better between 5 and 20 metres, theexternal surface of said rigid cylindrical pieces constituting saidsealed partition 5 or said cooling jig 7 being in continuous contactwith said envelope 2. The expression “continuous contact” needs to beunderstood that said contact is embodied on the entire circumference ofthe perimeter of the cross section of said envelope.

[0111]FIGS. 5, 6 and 7 show at each of the levels a, b, d and erespectively, for each of the circular, oval or rectangular envelopesand considerably amplified, deformations generated by the differentialpressure between the inside of the device and the ambient environmentbetween two sealed partitions respectively localised at the levels a ande. The differential pressure exerted on the envelope 2 is due to thedifference of density of the insulation material with respect to the seawater, said density generally being approximately between 0.8 and 0.85.Thus, by way of illustration, if a riser portion 11 is considered as 100m for an insulation material with a density 0.8, the differentialpressure between the top and the bottom shall be 0.2 Mpa, the lowportion (level d, FIG. 4) of said riser being in depression whereas thetop portion shall be in excess pressure. This shall result in a warping12 of the external envelope 2 whose result is approximately comparablein each of the configurations according to FIGS. 5, 6 and 7. Thedepression at the bottom portion shall tend to contract the envelope, asillustrated between the plane e and the plane d where the section isminimum, so as to then increase towards a maximum at b and then decreasetowards the nominal section imposed by the membrane 11. Depending on thebundle type, the deformations are shown in the planes a-b-c-d-e relatingto FIGS. 5, 6 and 7.

[0112] These warpings of the external envelope shall generate transferstowards the top of the semi-fluid or pasty insulation complex whichrisks harming the proper behaviour of the insulating material or evendestroy it as this type of insulation material subject to migrationremains fragile and is ill-adapted to withstand internal shearingscreated by the internal migrations.

[0113] In the case of FIG. 5 showing the circular envelope made ofthermoplastic material, the expansion at b is significant, but thecontraction observed at d remains extremely small as the existingdepression has fewer repercussions on the final shape.

[0114] Added to this phenomenon of transferring fluid upwards is thephenomenon of breathing as described previously, this phenomenon beingdue to the temperature variations of the internal pipes which generatevolume variations mainly inside the insulation complex which amplifywarpings, especially in the top portion.

[0115] When a transfer of the material of said insulation coveringoccurs by migration in said longitudinal direction ZZ′ and generallyfrom the bottom to the top in a case where said pipe is a riser or issloping, the shape of the perimeter of the cross section of saidenvelope is not uniform along the longitudinal axis of symmetry ZZ′ andsaid fixed shape of the perimeter of the cross section of said sealedpartition then corresponds to the shape of the cross section of saidenvelope before said transfer of material, that is when said insulationcovering is uniformly distributed around said pipe along saidlongitudinal axis ZZ′ and when said shape of the cross section of theenvelope along said longitudinal axis is also uniform.

[0116] When deformations of the envelope and the shape of the externalsurface of the insulation covering occur, the shape of the perimeter ofsaid cross section of the envelope generally remains symmetrical withrespect to said two axes XX′, YY′ perpendicular to each other and tosaid longitudinal axis of symmetry ZZ′ of the envelope.

[0117] In one preferred embodiment, the centralising jigs and coolingjigs are advantageously embodied similarly to a bicycle wheel as shownon FIGS. 21-24. Said jig is constituted by a wheel rim, a hub and spokesembodied preferably continuously as a filament winding.

[0118] A filament winding is understood to be a product obtained from aresistant fibre, preferably a carbon or glass fibre impregnated with acomposite product, such as epoxy resin, and preferably placedcontinuously tensed before the resin is reticulated.

[0119] Said wheel rim and said hub are preferably produced continuouslyfrom a flat steel strip.

[0120] Production is made from a wider strip and is folded depending onthe shape, such as rectangular, shown on FIG. 21. Additional stiffeners(not shown) are advantageously added to provide the unit with greatrigidity. The wheel rim 33 and its hub 32 are positioned with respect toeach other with the aid of a temporary device (not shown) and thecomposite strip impregnated with resin and kept in tension issuccessively passed around a hooking element of the wheel rim and thenan element for hooking the hub, and so on so as to constitute theinterlocking of spokes which shall constitute the resistant linkingbetween said wheel rim and said hub. It shall be noted that themechanical operating mode is similar to that of a bicycle wheel as,under a vertical load, the wheel rim works on compression, but all thespokes work on tension. The technique for producing a composite stripimpregnated with resin is known under the term of “pulltrusion” whichsignifies “traction/extrusion” and shall advantageously be associatedwith a handling robot which shall automatically carry out “knitting”around the support hooking elements of the wheel rim and the hub so asto constitute the spokes.

[0121] The cooling/centralising jig has been shown in a circular form,but its shape can also be approximately oval or rectangular with roundededges, but in this case the distribution of the spokes shall no longerbe uniform, certain zones needing to be strengthened so as to havesufficient resistance in all directions.

[0122] When the device of the invention has an envelope with arectangular cross section, the shape of this section is subject to highstresses in the high agitation zones close to the surface. This is whyin this case it is advantageous to provide, as shown on FIGS. 18 and 19,an external screen 21 providing it with a circular shape, said screen inaddition then being equipped on its external surface with ahelical-shaped antivortex stabilisation element 22. The device of theinvention with a envelope having a rectangular cross section shown onFIG. 18 is rendered integral with the external screen by rubber flexiblelinks 23.

[0123] The sealed partitions, centralising jigs 6 and the cooling jigs 7are preferably embodied from resistant materials not conducting largeamounts of heat, such as thermoplastic materials, possibly reinforced,composite materials or even made partially of metal and advantageouslybeing a combination of these techniques.

[0124] The largest diameters of the cross sections of the sealedpartitions, centralising jigs and cooling jigs is between about 1 and1.5 m, indeed 2 m in accordance with the overall size of the devices ofthe invention, also corresponding to envelope thickness of about between15 and 40 mm in the case of flexible polyethylene or polypropylenethermoplastic envelopes and between 5 and 8 mm in the case of semi-rigidsteel or composite envelopes and pipe diameters of about between 100 mmand 400 mm.

[0125] The assembling of unit sections 11 so as to form a continuousbundle of several kilometres can be carried out as follows. First ofall, a first section is produced with a length, say, of 100 m as shownon FIG. 14 and is equipped with its sealed partitions. In order to dothis, the internal pipes are produced from 12 m tube lengths weldedend-to-end and are then gradually the centralising and cooling jigs areinstalled, both being equipped for example with small wheels or runnersat their lower portion. Then the unit is inserted into the externalenvelope 2 by pushing the latter which has been produced as a singleelement or by the end-to-end joining of envelope units measuring 12 m,24 m or more, said end-to-end joining being preferably effected far fromthe extremity of the internal pipes. When the external envelope is inplace, said sealed partitions 5 are installed at each extremity wherethey are been rendered integral with the envelope 2 and the pipes 4 andthe insulation material is injected between the sealed partitions. Careshall be taken to allow on the side which needs to be lengthened theexternal envelope to project by a certain length, such as 20 cm, and theinternal pipes 4 for example, the first by 1 m and the second by 1.5 m,so that the zones where the end-to-end joinings to be effected bywelding are offset with respect to one another which shall permit accessto the welding and control equipment. Then the prefabricated sectionshall be pulled towards the sea so as to free the working zone and thenthe next section is produced similarly. When the external envelope isplaced around the new section, it is placed opposite with the envelopeon stand-by at one extremity of the preceding section and then welded.At the other extremity, a sealed partition 5 is installed and renderedintegral with said external envelope and the pipes, and then filling ofthe insulation material is carried out. Care shall be taken to allow thepipes 4 to project with a slight offset with respect to the externalenvelope as described above so as to facilitate the control and weldingoperations and the operation is restarted until a sufficient length isobtained.

[0126] If electric or umbilicate cables need to be installed inside thedevice, an additional pipe playing the role of a sheath shall be addedand the cable shall only be pulled through said sheath after thecomplete assembling of the full sheath length which may reach severalkilometres.

[0127] In one preferred version of the invention, the insulation complexis advantageously embodied from a reticulated gel possessing greatstability, such as a polyurethane compound which reticulation creatingan approximately continuous gel plays the role of a matrix within whichlocated is a dispersed liquid such as paraffin, gas oil or any othercompound possessing a low level of heat conductivity. Advantageously,during production of the complex, solid compounds shall be incorporatedwith said complex, said complexes being glass micro-spheres whose roleis to reduce the heat conductivity of the complex or fibrous matriceswhose role is to reduce the convection of the particles-remaining in aliquid state inside said insulation complex.

[0128] The various components are then mixed and energetically squeezedso as to obtain a homogenous compound which can then be injected inliquid form and thus fill the entire section limited by two consecutivesealed membranes. Prior to injection of the fluid insulation material,advantageously a vacuum shall be created in the section so as to avoidany pocket of residual gas. The vacuum created shall result in theenvelope locally imploding but the latter shall resume its initial shapeas soon as the sufficient required fluid quantity has been injected. Ofcourse, precautions shall be taken to dimension the centralising andcooling jigs and bring them sufficiently close together so that thistemporary implosion has no significant repercussions on the behaviour ofthe external envelope.

[0129] The injected homogenised product is found in a liquid stateduring the filling phase and after reticulation of the binder istransformed into a jellified matrix inside which the otherconstituent(s) are imprisoned remaining in a liquid state or also in agel state, which significantly reduces any convection phenomena.

[0130] The binding components shall preferably be polyurethanes so thatpolymerisation only starts after several hours, such as a minimum periodof between 6 and 8 hours which, together with reasonable pumping andmixing techniques, makes it possible within this period of time toembody devices 1 m in diameter in unit sections measuring about 100 m.

[0131] It is also possible to reduce the unit length or increase it byusing smaller or larger injection means, or even use components,possibly added with retarders whose opening time, that is the timeduring which it can be implemented, is shorter or longer, the main pointbeing that the entire injection operation needs to be ended before thereticulation or jellification reaction of the binder is initiatedsignificantly.

[0132] By proceeding in this way, filling of the bundle is considerablysimplified as the complicated tasks of the prior art are avoided, theseconsisting of installing absorbent matrices and causing the insulationfluid to percolate or even of hot-injecting an insulation complex, suchas paraffin, subject to significant retraction when it moves from aliquid state to a solid state.

1. Heat insulation device (1) for at least one sub-marine pipe (4)comprising: a heat insulation covering (3) surrounding said pipe(s) (3),said covering being covered with a sealed protective envelope (2), andsaid envelope having a tubular shape and a longitudinal axis of symmetry(ZZ′), said insulation covering (3) including a material subject tomigration and said envelope (2) being constituted by a flexible orsemi-rigid material able to remain in contact with the external surfaceof said insulation covering (3) when the latter warps. said device beingcharacterised in that it includes: at least two sealed transversalpartitions (5), each of said partitions being constituted by a closedrigid structure traversed by said pipe(s) and integral with the latterand integral at its periphery with said envelope, and at least onecentralising jig (6) and preferably a plurality of centralising jigs (6)placed preferably at regular intervals between said two successivesealed partitions along said longitudinal axis (ZZ′), each centralisingjig (6) being constituted by a rigid piece integral with said pipe(s)and having a shape permitting a limited radial movement of said envelope(2) on contraction and on expansion with regard to said centralising jig(6), said rigid piece of said centralising jig (6) having an externalcylindrical surface (6 ₄) in which the perimeter of the cross sectionstands back with respect to that of said sealed partition (5) and limitsthe warpings of said envelope by a direct mechanical stop on at leasttwo opposing points (2 ₁-2 ₂,2 ₃-2 ₄) of the perimeter of the crosssection of said envelope (2)
 2. Heat insulation device according toclaim 1, characterised in that each said sealed transversal partition(5) is constituted by a cylindrical piece having a cross section whoseperimeter has the same fixed shape as that of said cross section of theenvelope (2) in the absence of warping.
 3. Device according to one ofclaims 1 to 2, characterised in that said transversal partitions arespaced, preferably at regular intervals, along said longitudinal axis(ZZ′) by a distance of between 50 and 200 metres.
 4. Device according toone of claims 1 to 3, characterised in that it includes at least onecentralising jig (6) and preferably a plurality of centralising jigs (6)preferably placed at regular intervals between two of said successivesealed partitions (5) along said longitudinal axis (ZZ′), eachcentralising jig (6) being constituted by a rigid piece integral withsaid pipe(s) and having a shape permitting a limited movement of saidenvelope (2) on contraction and on expansion with regard to saidcentralising jig (6).
 5. Device according to claim 4, characterised inthat said centralising jig (6) is constituted by a rigid piecepreferably with a cylindrical external surface (6 ₄), the perimeter ofthe cross section standing back with respect to that of said sealedpartition (5) and limits the deformations of said envelope by a directmechanical stop of the latter on said second rigid piece (6) on, atleast two opposing points (2 ₁-2 ₂, 2 ₃-2 ₄) of the perimeter of thecross section of said envelope (2).
 6. Device according to claim 4 or 5,characterised in that said movement of the envelope (2) opposite saidcentralising jig (6) represents a variation of between 0.1 and 10% andpreferably 0.1 to 5% of the distance between two opposing points (2 ₁-2₂, 2 ₃-2 ₄) of the perimeter of the cross section of said envelope. 7.Device according to one of claims 4 to 6, characterised in that saidrigid piece constituting said centralising jig (6) has one portion ofits extreme surface sufficiently standing back with respect to thesurface of the envelope and/or has perforations traversing it so as tocreate a space (6 ₂) which allows the transfer of the materialconstituting said insulation covering (2) through said centralising jig(6).
 8. Device according to claim 7, characterised in that said crosssection of said centralising jig (6) has the shape of a rectangle whoseangles are truncated into cants (6 ₃).
 9. Device according to one ofclaims 4 to 8, characterised in that it comprises a plurality of saidcentralising jigs (6) and two successive centralising jigs are spacedalong said longitudinal axis (ZZ′) of the envelope by a distance ofbetween 2 and 5 metres.
 10. Device according to claims 8 or 9,characterised in that it includes a plurality of cooling jigs (7) placedalong said longitudinal axis (ZZ′) of the envelope preferably at regularintervals, two successive cooling jigs (7) being further spaced bybetween 20 and 50 metres.
 11. Device according to one of claims 1 to 10,characterised in that said rigid piece constituting said centralisingjig or said cooling jig includes an open structure formed by spokes (31)arranged radially between a hub (32) constituted by a cylindricalchamber surrounding said pipe(s) and a wheel rim (33) constituting thecontact surface of said jig with said envelope
 12. Device according toone of claims 1 to 11, characterised in that said envelope (2) defines aperimeter having two axes of symmetry (XX′) and (YY′) perpendicular toeach other and to said longitudinal axis (ZZ′).
 13. Device according toclaims 12, characterised in that the shape of said cross section of theenvelope is circular
 14. Device according to claim 12, characterised inthat the shape of said cross section of the envelope is oval
 15. Deviceaccording to claim 12, characterised in that the shape of said crosssection of the envelope is rectangular and preferably with roundedangles.
 16. Device for heat-insulating a bundle of sub-marine pipes,characterised in that it includes a device according to one of claims 1to 15 including at least two of said sub-marine pipes placed in parallel17. Device according to claim 16, characterised in that said sealedpartitions (5), the cooling jig (7) and centralising jig (6) keep atleast two of said sub-marine pipes (4) at a fixed distance from eachother
 18. Working unit heat insulation device so as to obtain a deviceaccording to one claims 1 to 17 via the end-to-end assembling of saidunit heat insulation devices, characterised in that it includes: one orall the sub-marine pipe unit elements instead of said sub-marinepipe(s), and an insulation covering (3), said protective envelope (2) asdefined in claims 1 to 17, each said unit element including at, at leastone of its extremities or at each of its extremities, said sealedpartition (5) and said centralising jigs (6) and preferably furthercooling jigs (7) as defined in claims 1 to 17 and disposed between twosuccessive sealed partitions.
 19. Method for heat-insulating at leastone sub-marine pipe, characterised ion that heat insulation devices areembodied according to claim 18 and assembled end-to-end
 20. Methodaccording to claim 20, characterised in that said insulation material isa complex including various components which are mixed and then injectedin a liquid state into the various compartments delimited by two of saidsuccessive sealed partitions and said insulation material is transformedinto a gel via the reticulation, of at least one of its components